Solvent-free, hot melt adhesive composition comprising a controlled distribution block copolymer

ABSTRACT

A novel solvent-free, hot melt adhesive composition suitable for bonding a polar leather layer to a non-polar substrate is claimed. The composition comprises a block copolymer having at least one mono alkenyl arene polymer block and at least one controlled distribution copolymer block of at least one conjugated diene and at least one mono alkenyl arene, a hydrogenated tackifying resin, a resin compatible with the mono alkenyl arene blocks, optionally a functionalized poly(alkylene) resin, and stabilizers and/or auxiliaries. A process for bonding a polar leather layer to a non-polar substrate by application of the novel solvent-free, hot melt adhesive composition is also provided.

FIELD OF THE INVENTION

The present invention relates to a solvent-free hot melt adhesivecomposition suitable for bonding a polar leather layer to a non-polarsubstrate, its use, a process of bonding a polar leather layer to thenon-polar substrate using the solvent-free, hot melt composition and tocomposed leather articles wherein the polar leather and non-polarsubstrate are bonded by the solvent-free hot melt adhesive composition.

More particularly, the invention relates to a solvent-free, hot meltadhesive composition suitable for bonding footwear components and tofootwear so obtained.

BACKGROUND OF THE INVENTION

Adhesive compositions for bonding footwear are known in the art. Suchknown compositions comprise significant amounts of organic solvents. Dueto increasingly stringent regulations from health, safety, andenvironmental authorities said organic solvents have to be eliminated.Unfortunately, the number of alternative adhesive compositions, whichare suitable for bonding highly non-polar footwear components, such asbonding synthetic polymeric shoe soles to polar components such asleather uppers, is limited. In addition, the conventional bondingtechnology requires a pre-treatment of the surface of the non-polarsubstrates in order to obtain an adequate bonding with a primer. This isessential when using highly non-polar synthetic footwear components,made from e.g. polyolefins or styrenic block copolymers, andparticularly hydrogenated styrenic block copolymers, e.g. KRATON® G-2705block copolymer compositions.

An improved solvent-free adhesive compositions for bonding a polarleather layer to a non-polar substrate layer was disclosed in co-pendingapplication EP02016728.4, which shows a combination of excellent bondingproperties and more reliable applicability and processability and loweroperational costs, e.g. by operating at lower processing temperatures orin an one step process, enabling shorter cycle times. The polymersdescribed therein are grafted with maleic anhydride. These compositionshave relative high HM (high-molecular) viscosity and need highapplication temperatures of about 230 to 260° C.

Now a novel anionic block copolymer based on mono alkenyl arene endblocks and controlled distribution mid blocks of mono alkenyl arenes andconjugated dienes has been discovered and is described in copending,commonly assigned U.S. patent application Ser. No. 60/355,210, entitled“NOVEL BLOCK COPOLYMERS AND METHOD FOR MAKING SAME”. Methods for makingsuch polymers are described in detail in the above-mentioned patentapplication.

There is need to a solvent-free, hot melt adhesive composition suitablefor bonding a polar leather layer to a non-polar substrate thatpossesses lower HM viscosity and needs application temperatures below230° C. At the same time the required good bonding between thecomponents must be maintained for a sufficient long time, i.e.sufficiently lifetime of the produced shoes, leather suitcases, composedleather sporting articles such as golf bags and horse saddles, fashionarticles (belts, handbags, briefcases). An object of the presentinvention is therefore to provide said solvent-free adhesivecomposition. Another object of the present invention is to provide aprocess for the manufacturing of composed products, comprising a polarleather component bonded to a non-polar synthetic or polymeric substratecomponent, and use of said solvent-free adhesive composition.

These and other objects were obtained by providing a new solvent-freehot melt adhesive composition.

SUMMARY OF THE INVENTION

Accordingly the invention relates to a solvent-free, hot melt adhesivecomposition suitable for bonding a polar leather layer to a non-polarsubstrate, comprising:

-   (a) a block copolymer having at least one A block and at least one B    block, wherein:    -   (i) each A block independently is a mono alkenyl arene polymer        block and each B block independently is a controlled        distribution copolymer block of at least one conjugated diene        and at least one mono alkenyl arene;    -   (ii) each A block having an average molecular weight between        about 3,000 and about 60,000 and each B block having an average        molecular weight between about 30,000 and about 300,000;    -   (iii) each B block comprises terminal regions adjacent to the A        block that are rich in conjugated diene units and one or more        regions not adjacent to the A blocks that are rich in mono        alkenyl arene units;    -   (iv) the total amount of mono alkenyl arene in the block        copolymer is about 20 percent weight to about 80 percent weight;        and    -   (v) the weight percent of mono alkenyl arene in each B block is        between about 10 percent and about 75 percent;-   (b) a hydrogenated hydrocarbon tackifying resin, with a softening    point lower than 140° C., preferably lower than 100° C. and more    preferably lower than 90° C., in a weight proportion of 30 to 150    parts by weight of tackifying resin per 100 parts per weight of    block copolymer and preferably from 50 to 120 parts by weight per    100 parts by weight of block copolymer;-   (c) a resin which is compatible with the mono alkenyl arene blocks,    having a softening point lower than 140° C. and preferably lower    than 110° C., in a weight proportion of from 10 to 80 parts by    weight and preferably from 20 to 60 parts by weight of resin per 100    parts by weight of block copolymer;-   (d) optionally a melt flow improving poly(alkylene) resin, which is    functionalized, in a weight proportion of from 0 to 30 parts by    weight, and preferably from 5 to 20 parts by weight per 100 parts by    weight of block copolymer, and-   (e) stabilizers and/or additional auxiliaries in a weight proportion    of from 0.1 to 1 part by weight per 100 parts by weight of block    copolymer.

DETAILED DESCRIPTION OF THE INVENTION

Examples of non-polar substrates are compositions, particularly for shoesoles (or midsoles), comprising inter alia: vinylarene/conjugated dieneblock copolymers such as KRATON® D copolymers, hydrogenatedvinylarene/conjugated diene block copolymers such as KRATON® Gcopolymers, vinylarene/ conjugated diene random copolymers, naturalrubbers, poly(vinylarene), polyolefin, EVA copolymer, and/or mixturesthereof, optionally in admixture with oils and other auxiliaries.

The present invention makes use of novel compositions. The combinationof (1) a unique control for the monomer addition and (2) the use ofdiethyl ether or other modifiers as a component of the solvent (whichwill be referred to as “distribution agents”) results in a certaincharacteristic distribution of the two monomers (herein termed a“controlled distribution” polymerization, i.e., a polymerizationresulting in a “controlled distribution” structure), and also results inthe presence of certain mono alkenyl arene rich regions and certainconjugated diene rich regions in the polymer block. For purposes hereof,“controlled distribution” is defined as referring to a molecularstructure having the following attributes: (1) terminal regions adjacentto the mono alkenyl arene homopolymer (“A”) blocks that are rich in(i.e., have a greater than average amount of) conjugated diene units;(2) one or more regions not adjacent to the A blocks that are rich in(i.e., have a greater than average amount of) mono alkenyl arene units;and (3) an overall structure having relatively low blockiness. For thepurposes hereof, “rich in” is defined as greater than the averageamount, preferably greater than 5% the average amount. The relativelylow blockiness can be shown by either the presence of only a singleglass transition temperature (“Tg,”) for the controlled distributionpolymer block intermediate between the Tg's of either monomer alone,when analyzed using differential scanning calorimetry (“DSC”) thermalmethods or via mechanical methods, or as shown via proton nuclearmagnetic resonance (1H-NMR) methods. The potential for blockiness canalso be inferred from measurement of the UV-visible absorbance in awavelength range suitable for the detection of polystyryl lithium endgroups during the polymerization of the B block. A sharp and substantialincrease in this value is indicative of a substantial increase inpolystyryl lithium chain ends. In this process, this will only occur ifthe conjugated diene concentration drops below the critical level tomaintain controlled distribution polymerization. Any styrene monomerthat is present at this point will add in a blocky fashion. The term“styrene blockiness”, as measured by those skilled in the art, usingproton NMR, is defined to be the proportion of S units in the polymerhaving two S nearest neighbors on the polymer chain. The styreneblockiness is determined after using 1H-NMR to measure two experimentalquantities as follows:

First, the total number of styrene units (i.e. arbitrary instrumentunits which cancel out when ratioed) is determined by integrating thetotal styrene aromatic signal in the 1H-NMR spectrum from 7.5 to 6.2 ppmand dividing this quantity by 5 to account for the 5 aromatic hydrogenson each styrene aromatic ring.

Second, the blocky styrene units are determined by integrating thatportion of the aromatic signal in the 1H-NMR spectrum from the signalminimum between 6.88 and 6.80 to 6.2 ppm and dividing this quantity by 2to account for the 2 ortho-hydrogens on each blocky styrene aromaticring. The styrene blockiness is the percentage of blocky styrene tototal styrene units:Blocky %=100 times (Blocky Styrene Units/Total Styrene Units)

Expressed thus, Polymer-Bd-S-(S)n-S-Bd-Polymer, where n is greater thanzero is defined to be blocky styrene. It is preferred that theblockiness index be less than about 40. For some polymers, havingstyrene contents of ten weight percent to forty weight percent, it ispreferred that the blockiness index be less than about 10.

In a preferred embodiment of the present invention, the subjectcontrolled distribution copolymer block has three distinctregions—conjugated diene rich regions on the end of the block and a monoalkenyl arene rich region near the middle or center of the block(mid-block). Preferred copolymers have the general configuration A-B,A-B-A, (A-B)n, (A-B)n-A, (A-B-A)nX, or (A-B)nX, wherein n is an integerfrom 2 to 30, preferably from 2 to 6, X is coupling agent residue andwherein A and B have the meaning defined hereinbefore. Best results areobtained with copolymers wherein at least one of A and B arehydrogenated. Preferably, the copolymers have a mid-block with 15 to 35%alkenyl arene, particularly styrene. More preferred these copolymershave a mid-block with 20–30% styrene.

In a preferred embodiment the solvent-free, hot melt adhesivecomposition further comprises at least one C block, wherein each C blockis a polymer block of one or more conjugated dienes, having an averagenumber molecular weight between 2,000 and 200,000.

To the adhesive composition an acid compound or its derivative may begrafted and/or it may be reacted with a silicon or boron-containingcompound, with at least one ethylene oxide molecule, with at least onecarbon dioxide molecule and/or which has been metallated with an alkalimetal alkyl.

Preferably, the A block has a glass transition temperature of +80° C. to+110° C. and the B block has a glass transition temperature of above−60° C. to less than the glass transition temperature of the A block,preferably between −40° C. and +30° C.

The Young's modulus preferably is below 25% elongation of less than2,800 psi (20 MPa) and the rubber modulus or slope is between 100 and300% elongation of greater than 70 psi (0.5 MPa).

Preferably, at least one of the components of the block copolymer is atleast partially hydrogenated, more preferably less than 10% of the arenedouble bonds are reduced and at least 90% of the conjugated diene doublebonds are reduced.

Anionic, solution copolymerization to form the controlled distributioncopolymers of the present invention can be carried out using, to a greatextent, known and previously employed methods and materials. In general,the copolymerization is attained anionically, using known selections ofadjunct materials, including polymerization initiators, solvents,promoters, and structure modifiers, but as a key feature of the presentinvention, in the presence of a certain distribution agent. Suchdistribution agent is, in preferred embodiments, a non-chelating ether.Examples of such ether compounds are cyclic ethers such astetrahydrofuran and tetrahydropyrane and aliphatic monoethers such asdiethyl ether and dibutyl ether. Other distribution agents include, forexample, ortho-dimethoxybenzene or “ODMB”, which is sometimes referredto as a chelating agent.

An important aspect of the present invention is to control themicrostructure or vinyl content of the conjugated diene in thecontrolled distribution copolymer block. The term “vinyl content” refersto the fact that a conjugated diene is polymerized via 1,2-addition (inthe case of butadiene—it would be 3,4-addition in the case of isoprene).Although a pure “vinyl” group is formed only in the case of 1,2-additionpolymerization of 1,3-butadiene, the effects of 3,4-additionpolymerization of isoprene (and similar addition for other conjugateddienes) on the final properties of the block copolymer will be similar.The term “vinyl” refers to the presence of a pendant vinyl group on thepolymer chain. When referring to the use of butadiene as the conjugateddiene, it is preferred that about 20 to about 80 mol percent of thecondensed butadiene units in the copolymer block have 1,2 vinylconfiguration as determined by proton NMR analysis. For selectivelyhydrogenated block copolymers, preferably about 30 to about 70 molpercent of the condensed butadiene units should have 1,2 configuration.For unsaturated block copolymers, preferably about 20 to about 40 molpercent of the condensed butadiene units should have 1,2-vinylconfiguration. This is effectively controlled by varying the relativeamount of the distribution agent.

The solvent used as the polymerization vehicle may be any hydrocarbonthat does not react with the living anionic chain end of the formingpolymer, is easily handled in commercial polymerization units, andoffers the appropriate solubility characteristics for the productpolymer. For example, non-polar aliphatic hydrocarbons, which aregenerally lacking in ionizable hydrogens make particularly suitablesolvents. Frequently used are cyclic alkanes, such as cyclopentane,cyclohexane, cycloheptane, and cyclooctane.

Starting materials for preparing the novel controlled distributioncopolymers of the present invention include the initial monomers. Thealkenyl arene can be selected from styrene, alpha-methylstyrene,para-methylstyrene, vinyl toluene, vinylnaphthalene, and para-butylstyrene or mixtures thereof. Of these, styrene is most preferred and iscommercially available, and relatively inexpensive, from a variety ofmanufacturers. The conjugated dienes for use herein are 1,3-butadieneand substituted butadienes such as isoprene, piperylene,2,3-dimethyl-1,3-butadiene, and 1-phenyl-1,3-butadiene, or mixturesthereof. Of these, 1,3-butadiene is most preferred. As used herein“butadiene” refers specifically to “1,3-butadiene”.

Other important starting materials for anionic copolymerizations includeone or more polymerization initiators. In the present invention suchinclude, for example, alkyl lithium compounds and other organo lithiumcompounds such as s-butyl lithium, n-butyl lithium, t-butyl lithium,amyl lithium and the like, including di-initiators such as thedi-sec-butyl lithium adduct of m-diisopropenyl benzene. Of the variouspolymerization initiators, s-butyl lithium is preferred.

Polymerization conditions to prepare the novel copolymers of the presentinvention are typically similar to those used for anionicpolymerizations in general. In the present invention polymerization ispreferably carried out at a temperature of from −30 to +150° C., morepreferably +10 to +100° C., and most preferably, in view of industriallimitations, 30 to 90° C. It is carried out in an inert atmospherepreferably nitrogen, and may also be accomplished under pressure withinthe range of from about 0.5 to about 10 bars. This copolymerizationgenerally requires less than about 12 hours, and can be accomplished infrom about 5 minutes to about 5 hours, depending upon the temperature,the concentration of the monomer components, the molecular weight of thepolymer and the amount of distribution agent that is employed.

The component (b) is actually blended with the block copolymer component(a) to provide tack. Examples of hydrogenated hydrocarbon tackifyingresins which may be suitable applied in the adhesive compositions of thepresent invention are hydrogenated rosin esters, and more in particularthe glycerol ester of hydrogenated rosin or pentaerythritol ester ofhydrogenated rosin (e.g. FORAL™ 85E, FORALYNE™ 85E, or FORAL™ 105) orhydrogenated hydrocarbon resins (e.g., such as REGALITE™ R resins orARKON M resins or ESCOREZ™ 5000 series or STABILITE™ resins).Preferably, diglycerol ester of highly hydrogenated resin (FORAL™ 85-E)is used as component (b) and more preferably in an amount of from 70 to100 PHR.

As resin, which is compatible with resinous terminal block portions ofthe block copolymer (component c), an aromatic hydrocarbon resin can beused. Useful resins include coumarone-indene resins, poly(alpha-methylstyrene) resins, poly styrene resins or vinyl toluene-(alpha-methylstyrene) copolymers. Examples of aromatic hydrocarbon resins useful inthe adhesive composition of the present invention are AMOCO 18 seriesresins, KRISTALEX™ series resins (e.g. KRISTALEX™ F100 or 3115), whichare composed of alpha-methyl styrene (EASTMAN), PICCOTEX™ series resinswhich are composed of alpha-methyl styrene and vinyl toluene (EASTMAN),NEVCHEM™ (NEVILLE) and PICCO™ 6000 (EASTMAN) series resins which arecomposed of aromatic hydrocarbons, CUMAR™ series resins, e.g. CUMAR™LX509 (NEVILLE) which are composed of coumarone-indene resins, HERCURES™A101 resin (aromatic resin derived from aromatic petroleum (EASTMAN). Aspreferred resin component (c) HERCURES™ A101 resin or KRISTALEX™ F100resin are used.

As optional component (d) can be used homopolymers of propylene or oneor more crystalline copolymers of propylene, which contain 50 wt % ormore propylene (e.g. ADFLEX™ copolymers, i.e. copolymers made ofpropylene and a further olefin by the CATALLOY™ process), or mixtures ofthe hereinbefore mentioned (co)polymers, which have been acid graftedand preferably with maleic acid or maleic anhydride. In preferredsolvent-free, hot melt adhesive compositions said propylene (co)polymeris included more preferably in amounts of 5 to 20 parts by weight per100 parts by weight of block copolymer. Preferred propylene copolymersare PP QESTRON™ KA 802A, PP QESTRON™ 805A, which are maleic anhydridegrafted heterophasic PP copolymers of BASELL.

As component (e) can be used stabilizers, which are known from e.g. U.S.Pat. No. 4,835,200. More in particular phenolic antioxidant (IRGANOX™),benzotriazole ultraviolet inhibitor (TINUVIN™ P) and a hindered amineultraviolet inhibitor (TINUVIN™ 770) can be used to stabilize theformulation against degradation. Particularly preferred are hinderedphenols and more preferred less volatile hindered phenols such astetrakis[methylene-3,5-di-tert-butyl-4-hydroxy-hydrocinnamate]methane(IRGANOX™ 1010 antioxidant) or2(3,5-di-tert-butyl-4-hydroxy)-4,6-bis(N-octylthio)-1,3,3-triazine(IRGANOX™ 565 antioxidant). TINUVIN™ P and IRGANOX™ 1010 are known toshow synergistic effect in polymer stabilization.

It will be appreciated that the solvent-free, hot melt adhesivecomposition provides excellent bonding when applied at 150 to 230° C.Preferably, the bonding is provided when applying a temperature between170 and 200° C. Moreover the bonded polar leather—non-polar syntheticmaterial composites do not show any break upon repeatedly bendingcontrary to the composites made by using prior hot melt adhesivecompositions. Therefore the adhesive compositions of the presentinvention have been found to provide attractive flexing endurance orresistance to flexing to footwear.

It will be appreciated that another aspect of the present invention isformed by the use of hereinbefore specified solvent-free, hot meltadhesive compositions for bonding a polar leather layer to a non-polarsubstrate. In particular said use relates to the bonding of shoecomponents and components of other formed leather articles such assuitcases, sporting articles and fashion articles, formed from a leathercomponent and a synthetic polymeric non-polar component. More inparticular said use relates to the bonding of shoe uppers and soles. Ina more preferred use the shoe uppers are made of leather and the shoesoles are made of a non-polar polymeric material.

Moreover, the present invention is also relating to a process forbonding a polar leather layer to a non-polar synthetic polymeric layer,and more preferably shoe components, by the use of thehereinbefore-specified adhesive compositions of the invention. Suchprocess may, and preferably is automated.

It will be appreciated that another aspect of the present invention isformed by the composed formed articles, such as shoes, handbagssuitcases, derived from a polar leather component and a non-polarsynthetic component, which have been bonded to each other with ahereinbefore defined adhesive composition.

The invention is further illustrated by the following examples, howeverwithout restricting its scope to these specific embodiments.

EXAMPLE 1

Various controlled distribution copolymers of the present invention wereprepared according to the process claimed herein. All polymers wereselectively hydrogenated ABA block copolymers where the A blocks werepolystyrene blocks and the B block prior to hydrogenation was astyrene/butadiene controlled distribution block copolymer havingterminal regions that are rich in butadiene units and a center regionthat was rich in styrene units. The polymers were hydrogenated understandard conditions such that greater than 95% of the diene double bondsin the B block have been reduced.

The following describes the general procedure used to effectivelycontrol the distribution of the comonomers in the anioniccopolymerization of 1,3-butadiene (Bd) and styrene (S) in the presenceof diethyl ether (DEE). A number of tri-block copolymers weresynthesized stepwise in cyclohexane. DEE was used to control thedistribution of copolymerization of styrene and butadiene in the rubbermid-block. During the copolymerization step, a number of samples werecollected as the reaction progressed to enable 1H-NMR characterizationof the degree of comonomer distribution.

For Step I, an appropriate amount of polymerization grade cyclohexanewas charged to a well-mixed 227 liter stainless steel reactor vessel at30° C. Pressure in the reactor vessel was controlled with nitrogen gas.Styrene monomer was charged to the reactor at 30° C. 10 ml increments ofsec-butyl lithium (12 wt. %) were added to the reactor to titrate thecyclohexane and styrene monomer mixture. The titration endpoint wasdetermined with an on-line calorimeter. After titration, sec-butyllithium was then added to the reactor to initiate the anionicpolymerization of the living polystyrene blocks. The temperature wasallowed to increase to 55° C. and the reaction was carried out to 99.9%conversion of the styrene. This completed the first styrene block ofthis block copolymer, (S)-.

For Step II, an appropriate amount of polymerization grade cyclohexanewas charged to a well-mixed 492 liter stainless steel reactor vessel at30° C. First, all of the styrene monomer required in the Step IIreaction was charged to the reactor. Second, one-half of the butadienemonomer required in the Step II reaction was charged to the reactor.Third, an appropriate amount of diethyl ether was charged to thereactor. Fourth, 10 ml increments of sec-butyllithium (12% wt.) wereadded to the reactor to titrate the cyclohexane, styrene monomer,butadiene monomer and diethyl ether mixture. The titration endpoint wasdetermined with an on-line calorimeter. After titration of the Step IIrecatonts, the living polystyrene chains were transferred via nitrogenpressure from the Step I reactor vessel to the Step II reactor vessel toinitiate the Step II copolymerization reaction of styrene and butadieneat 30° C. Ten minutes after the initiation of the copolymerization, theremaining one-half of the butadiene monomer was dosed to the Step IIreactor at a rate that kept the overall polymerization rate nearlyconstant. The temperature was allowed to increase to 55° C. and thereaction was carried out to 99.9% conversion basis butadiene kinetics.This completed the addition of a styrene-butadiene randomized mid-blockto the Step I polystyrene block. The polymer structure at this point is(S)-(S/Bd)-.

For Step III, more styrene monomer was charged to the Step II reactorvessel at 55° C. to react with the living (S)-(S/Bd)-polymer chains. TheStep III reaction was maintained at near isothermal conditions until99.9% conversion of the styrene. The living polymer chains wereterminated by adding an appropriate amount (about 10% molar excess) ofhigh-grade methanol to the final reactor solution. The final polymerstructure was (S)-(S/Bd)-(S). All polymers were then selectivelyhydrogenated to produce linear ABA block copolymers where the A blockswere polystyrene blocks and the B block prior to hydrogenation was astyrene butadiene controlled distribution block having terminal regionsthat are rich in butadiene units and a center region that was rich instyrene units. The various polymers are shown in Table 1 below. Step IMW is the molecular weight of the first A block, Step II MW is themolecular weight of the AB blocks and Step III MW is the molecularweight of the ABA blocks. The polymers were hydrogenated such thatgreater than about 95% of the diene double bonds have been reduced.

This type of experiment was executed several times over a range ofvarying styrene-butadiene mid-block compositions. The followingdescribes the method used to characterize the polymer mid or “B” block.It is the nature of the polymerization that the polymer mid-block isformed after an initial styrene block. Since the polymer mid-block whichis formed in Step II cannot be analyzed in isolation, it must beanalyzed in combination with the Step I styrene block, and thecontribution of the Step I styrene block must be subtracted from the sumto determine the parameters which characterize the polymer mid-block.Four experimental quantities are used to calculate the percent styrenecontent in the polymer mid-block (Mid PSC) and the percent blockystyrene in the polymer mid-block (Mid Blocky). (Note: % BD12 for themid-block is measured directly with no need to correct a BD contributionfrom the Step I styrene block).

The total styrene mass in Step II is given by:33.4 wt % of 86.8 k=29.0 k styrene in Step IIThe styrene mass of the mid-block is found by subtracting the Step Istyrene mass from the styrene in Step II:29.0k−9.0k=20.0k styrene in mid-blockThe mass of the mid-block is given by subtracting the Step I MW from theStep II MW:86.8k−9.0k=77.8k mass if mid-blockThe “Mid PSC” is the percent of mid-block styrene relative to themid-block mass:100*20.0k mid-block styrene/77.8k mid-block mass=25.7 wt %The blocky styrene % and the Step II styrene mass gives the mass ofblocky styrene:33% of 29.0k=9.6k Step II blocky styreneThe Step I styrene block is subtracted from the mass of Step II blockystyrene to give the mass of blocky styrene in the mid-block:9.6k Step II blocky styrene−9.0k Step I styrene block=0.6kThe “Mid Blocky” is the percent of blocky styrene in the mid-blockrelative to the styrene in the mid-block:100*0.6k mid-block blocky styrene/20.0k mid-block styrene=3%

TABLE 1 Controlled Distribution Polymers % Step I Step Styrene PolymerMW Step II III in Step Styrene 1,2-BD PSC Number (k) MW (k) MW (k) IIBlockiness (%) (%) 25 9.1 89 97 25 0 36 39 27 7.5 70 77 25 3 36.1 40 287.8 39 — 25 16 36 39 26 7.3 43 50 37 0 36.7 47 where “MW (k)” =molecular weight in thousands and “PSC (%)” = wt % of styrene in thefinal polymer. “Styrene Blockiness” is for just the B block.

EXAMPLE 2 Hypothetical Preparation of a Hot Melt Adhesive

A typical solvent-free, hot melt adhesive composition according to thepresent invention comprises 125 parts by weight of the CD polymer, 100parts by weight of a tackifying resin (e.g., Foralyne 85E), 50 parts byweight of of a resin (e.g., Hercules A101) and 3 parts by weight of anantioxidant (e.g., Irganox 1010). Typical compositions may furthercomprise polypropylene.

The solvent-free, hot melt adhesive composition may be prepared using aMARIS™ 30VI, 30 mm corotating twin screw extruder. The gravimetricfeeders thereof, one for the polymer and two for the resin, can beequipped with a vibration tray. The processing of hot melts begins withpre-blending the polymer, the polypropylene if any and antioxidant. Thepre-blend may then be added to the extruder via the first feeding port.At the second and third feeding port, part of the resins (⅓ to ½ of thetotal amount of resin) may be added.

The hot melt strand may be cut on a GALA™ granulator with a die platetemperature of 130° C. and at a speed of 1500 rpm and cooled by water.

A hot melt adhesive composition prepared in line with the instructionsabove may be tested in line with common practice as applied by shoeproducers. For instance, the sole/upper bonding may be tested by meansof ROSSFLEX test bars (75×25×7 mm), which can be injection molded on a200 kW BATTENFELD™ BA 200/50 CD molding machine and subsequently cut intwo parts for use in the assembling lab test. Pre-buffed leather strapsof similar dimension can be used.

A hot melt dispenser, equipped with a 2 mm thick slit die (10 mm wide),may be used to manually apply a hot melt layer onto non-primed compoundtest bars. Suitable hot melt application temperatures vary from 260° to200° C. The adhesive application and bonding operation (including thepositioning of the test bar onto the leather strap and time tillapplying full pressure) should be kept as short as possible to preventthe hot melt from cooling down and as such keep the hot melt viscosityas low as possible.

After hot melt application, the test bars and leather straps may beimmediately pressed for 15 seconds at 12 kg/cm². In order to fix thebonds well, it may be necessary to apply pressure on the test assemblyuntil the bond has built up sufficient strength to avoid separation uponremoval from the press.

T-peel testing may be carried out according to the SATRA AM1 180° C.T-peel test after storing the samples to be tested for at least 24 hoursin a standard controlled environment at 21° C. and 65% relativehumidity. The Peel tests may be carried out using the ZWICK™ tensiletester and at a rate of 100 mm/sec until a bond length of 30 mm had beenpeeled.

EXAMPLE 3 Illustrative Example

A scouting experiment was conducted with CD polymer #25, in line withthe instructions of Example 2. The hot melt adhesive was compared withthe adhesive of co-pending application EP02016728.4, albeit that theblock copolymer of the comparative composition has a lower molecularweight and has been grafted with maleic anhydride.

Adhesion values were found for the composition according to theinvention that exceed the industry requirement of 5 N/mm and that areslightly higher than those obtained using the comparative composition(6.8 N/mm vs. 4.3 N/mm when applied on a standard non-primed solesubstrate at 230° C.). Further improvements in respect of melt viscositymay be had by using a DC polymer having a lower molecular weight.

1. A hot melt adhesive suitable for bonding a polar leather layer to anon-polar substrate, comprising: (a) a block copolymer having at leastone A block and at least one B block, wherein: (i) each A block is amono alkenyl arene polymer block and each B block is a controlleddistribution copolymer block of at least one conjugated diene and atleast one mono alkenyl arene; (ii) each A block having an averagemolecular weight between about 3,000 and about 60,000 and each B blockhaving an average molecular weight between about 30,000 and about300,000; (iii) each B block comprises terminal regions adjacent to the Ablock that are rich in conjugated diene units and one or more regionsnot adjacent to the A blocks that are rich in mono alkenyl arene units;(iv) the total amount of mono alkenyl arene in the block copolymer isabout 20 percent weight to about 80 percent weight; (v) the weightpercent of mono alkenyl arene in each B block is between about 10percent and about 75 percent; (vi) the styrene blockiness index of theblock B is less than 40 percent, said styrene blockiness index being theproportion of styrene units in the block B having two styrene neighborson the polymer chain; and wherein the block copolymer has a Young'smodulus below 25% elongation of less than 20 MPa and a rubber modulus orslope between 100 and 300% elongation of greater than 0.5 MPa; (b) ahydrogenated hydrocarbon tackifying resin, with a softening point lowerthan 140° C. in a weight proportion of 30 to 150 parts by weight oftackifying resin per 100 parts per weight of block copolymer; (c) aresin which is compatible with the mono alkenyl arene blocks, having asoftening point lower than 140° C., in a weight proportion of from 10 to80 parts by weight of resin per 100 parts by weight of block copolymer;(d) optionally a melt flow improving poly(alkylene) resin, which isfunctionalized, in a weight proportion of from 0 to 30 parts by weightper 100 parts by weight of block copolymer, and (e) stabilizers and/oradditional auxiliaries in a weight proportion of from 0.1 to 1 part byweight per 100 parts by weight of block copolymer.
 2. The hot meltadhesive of claim 1 wherein in the block copolymer mono alkenyl arene isstyrene and the conjugated diene is isoprene, butadiene, or a mixturethereof.
 3. The hot melt adhesive of claim 1 wherein in the blockcopolymer the conjugated diene is butadiene and wherein 20 to 80 molpercent of the condensed butadiene units in block B have1,2-configuration.
 4. The hot melt adhesive of claim 1 wherein the blockcopolymer has the general configuration A-B, A-B-A, (A-B)n, (A-B)n-A,(A-B-A)nX, or (A-B)nX, wherein n is an integer from 2 to 30, X iscoupling agent residue and wherein A and B have the meaning definedhereinbefore.
 5. The hot melt adhesive of claim 1 wherein component (b)comprises hydrogenated rosin esters or hydrogenated hydrocarbon resin,and is present in a weight proportion of from 50 to 120 parts by weightresin per 100 parts by weight of block copolymer.
 6. The hot meltadhesive of claim 1 wherein component (c) comprises an aromatichydrocarbon resin.
 7. The hot melt adhesive of claim 6 wherein component(c) comprises at least one of coumarone-indene resins,poly(alpha-methyl-styrene) resins, poly styrene resins, and vinyltoluene-(alpha-methyl-styrene) copolymers.
 8. The hot melt adhesive ofclaim 1 wherein the styrene blockiness index of the block B is less than10 percent.
 9. The hot melt adhesive of claim 1, wherein thehydrogenated hydrocarbon tackifying resin has a softening point of lowerthan 100° C. and is in a weight proportion of from 50 to 120 parts byweight of tackifying resin per 100 parts by weight of block copolymer.10. The hot melt adhesive of claim 1, wherein the resin which iscompatible with the mono alkenyl arene blocks has a softening pointlower than 110° C., and is in a weight proportion of from 20 to 60 partsby weight of resin per 100 parts by weight of block copolymer.